Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan

Abstract

ABSTRACT. One of the major, but often overlooked, challenges towards high end applications of nanocelluloses is to maintain their mechanical stability under hydrated conditions. As such, permanent covalent crosslinking or surface hydrophobization are viable solutions provided that neither processability nor interfibrillar bonding is compromised. Here we show an alternative based on physical crosslinking of nanofibrillated cellulose (NFC, also denoted as microfibrillated cellulose, MFC, and cellulose nanofibers, CNF) with chitosan for the preparation of transparent films. Transparency (~ 80 % throughout the visible spectrum) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the NFC/chitosan mixtures form easily processable hydrogels.A simple change in the environmental conditions (i.e. an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between NFC and chitosan over those with water, resulting effectively in crosslinking. Films of NFC/chitosan 80/20 w/w show excellent mechanical properties in the wet state, with a tensile modulus of 4 and 14 GPa at low (0.5 %) and large (16 %) strains, respectively and an ultimate strength of 100 MPa (with corresponding maximum strain of 28 %). Remarkably, a strength of 200 MPa (with maximum strain of 8%) is measured at 50 % air relative humidity. We expect that the proposed, simple concept opens new pathways toward NFC-based material utilization in wet or humid conditions, a challenge that has remained unresolved.

Increased functional properties and thermal stability of flexible cellulose nanocrystal/ZnO films

“…Those results are in line with previous reports in which it is shown that the tensile modulus of the nanopaper increases at expense of ductility when it is reinforced with stiff nanoparticles . In this framework, the improvement of the CNC-ZnO particle interaction by chemical modification of zinc oxide would lead to a more favourable stress-transfer across the nanopaper structure, increasing the fracture toughness (Toivonen et al, 2015). Performed mechanical tests confirm the high strength of fabricated nanopapers, which show higher Young modulus than many synthetic polymers such as polystyrene, polyethylene and polyethylene terephthalate (Briston, 1988).…”

A High‐Performance, Low‐Tortuosity Wood‐Carbon Monolith Reactor

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high tortuosity and complex flow channels, which may cause high flow resistance, specifically due to agglomeration when the reactant gas flows through the Ni catalysts. [34][35][36][37] Mechanically superstrong composites have been demonstrated by incorporating cellulose nanofibers. For example, transparent films based on cellulose nanofibers are promising replacements of plastics for biodegradable electronics.

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Novel chitin/chitosan-glucan wound dressing: Isolation, characterization, antibacterial activity and wound healing properties

“…The lack of applications of chitosan fibers were the poor mechanical and stability of dressing chitosan fibers/fabrics as well as to prepare 3D structure of chitosan has to be chemically cross-linked by different hazardous cross-linker (Lee et al, 2004;Schiffman and Schauer, 2007;Yang et al, 2005). Almost all studies of chitosan based wound dressing only used on form of fibers (micro/nano) (Annur et al, 2015;Schiffman and Schauer, 2007;Toivonen et al, 2015;Zhang et al, 2008), films (Ligler et al, 2001;Mi et al, 2006;Suginta et al, 2013;Yuan et al, 2007) or hydrogel (Jungst et al, 2015;Kumar et al, 2004;Suginta et al, 2013), but chitin/chitosan-glucan microfibers/nonwoven mats not been reported. Therefore, in the present research we dissolve the complex for the first time in green solvent, and to innovate complex-based wound dressing with improved the bacteria killing and to enhance the healing properties.…”